JPH06193742A - Ferromagnetic fluid seal centering ring - Google Patents

Abstract

PURPOSE: To hold a centering ring near a ferrofluidic seal released from a seal by bursting due to overpressurization by releasably attaching the centering ring to a ferrofluidic seal module comprising an annular magnet and pole pieces all assembled into a seal housing, and mounting the module about a shaft via the ring. CONSTITUTION: This ferrofluidic seal module 10 attached to a housing 28 axially surrounding a magnetically permeable shaft 12 comprises an annular magnet 18, annular pole pieces 14, 16 and a housing 100, and a centering ring 26 can be attached thereto. The centering ring 26 has an outer edge 33 which fits tightly within the housing 100 and an inner edge 31 which engages the shaft 12 when the module 10 is installed around the shaft 12, and mounting of the centering ring 26 to the shaft 12 assures a desired gap G between the inner edge 35 of each pole piece 14, 16 and the shaft 12. The centering ring 26 is removed after the module 10 has been centered.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to ferrofluidic seals and, more particularly, to centering a ferrofluidic seal about a shaft when the ferrofluidic seal is in place on the device in which it is used. It is related to the mechanism of.

[0002]

Ferrofluidic seals are commonly used to provide a hermetic seal against gases and other contaminants in applications where rotating shafts must be sealed. Ferrofluidic seals are used in computer magnetic disk storage units as a barrier between the motor area and the disk area to prevent contaminants from reaching the disk area. Also,
It is used for robot actuators designed for ultra-high vacuum processing of semiconductor wafers, for sealing rotating anodes in high vacuum environments, and for pumps in refineries and chemical plants.

Ferrofluidic seals can be used to seal any component that has a static or rotational relationship to another component. Such seals are typically mounted so that they remain stationary around the rotating shaft, but it is also possible to seal the stationary shaft around which the hub rotates. The seal operates mostly through the use of a ferrofluid in the gap between the rotating shaft and the surface of the stationary seal, which is desired to hold and concentrate the ferrofluid in the gap as a hermetic liquid O-ring. An annular magnet is included to provide a magnetic flux path. Ferrofluidic seals typically include an axially magnetized annular permanent magnet and a pair of magnetically permeable annular pole pieces sandwiching the magnet, the inner periphery of the pole pieces being the surface of the shaft. It extends toward and forms a narrow non-contact gap with it.

Ferrofluidic seals have been constructed and arranged to address a variety of sealing needs. A one-step ferrofluidic seal can be created by placing a single annular pole piece in magnetic communication with a single magnet in close proximity around a magnetically permeable shaft. The ferrofluid is caused by the magnetic field generated by the magnet to
Held in the gap of the shaft, this magnetic field follows a magnetic circuit that includes the magnet and pole pieces, the gap and the shaft. 1
In the staged seal, it is advantageous to use a second annular pole piece, also adjacent to the shaft, which is in magnetic communication with the other pole of the magnet. The gap between the second pole piece and the shaft is generally free of ferrofluid, but in a one-stage seal it enhances the magnetic flux across the gap in which the ferrofluid is retained to enhance the seal's It is designed to increase pressure performance.

Alternatively, a ferrofluid can be included in the gap between the second pole piece and the shaft to create a two-stage seal. Assigned to the applicant, 1991
US Pat. Nos. 5,018,751 and 198 issued May 28, 1985
U.S. Pat. No. 4,506,895, issued March 26, 1993, describes a two-stage ferrofluidic seal as described above.

In addition, the ferrofluidic seal can include any number of steps. That is, the seal may include a plurality of individual pole pieces, or the pole piece (s) may include a plurality of ridges and grooves, each ridge proximate the shaft. It is also possible to define an annular gap between the piece and the shaft. Ferrofluids are retained in some or all of these gaps,
A multi-stage ferrofluidic seal is formed.

Regarding the pole pieces of the ferrofluidic seal, and the relationship between the pole pieces, the bearings that support the shaft, and the other components of the ferrofluidic seal system, there are a number of different arrangements and designs. Embodiments exist. For example, the ridges and grooves can be formed in the shaft rather than the pole piece (s) to define a one-step or multi-step ferrofluidic seal. The pole piece (or one or more of some ridges in the pole piece) may have a taper, or may have a particular width, or have a different concentric radius than that of other ridges or pole pieces. You can Geometrical variability, such as these, in certain properties of the overall ferrofluidic seal configuration, such as life of certain gaps for retention of ferrofluid, favorable heat dissipation, high speed rotation of the shaft or hub. Prevents ferrofluid splattering, selectively retains ferrofluid in one or more annular gaps, and allows other properties to be tailored to the application.

Important to the proper operation of the ferrofluidic seal is the accurate mounting of the pole piece (s) concentrically with respect to the shaft. Inaccurate centering of the pole pieces around the shaft results in a non-uniform width of the resulting annular gap between the pole pieces and the shaft. Generally, the pole piece (s) are closest to the shaft, and centering about them is of paramount importance. However, other components forming the ferrofluidic seal may also be in close proximity to the shaft. For example, it is possible that an annular magnet is sandwiched by pole pieces, and the magnet and pole pieces all have the same inner diameter. It will be appreciated that it is important to center all components (particularly the closest component) of the ferromagnetic seal arrangement proximate the shaft. However, in the following,
"Seal" shall refer to a component of a ferrofluidic seal that is adjacent to the shaft and for which centering is important.

If the seal is not concentric with the shaft, the magnetic field does not follow a symmetrical path around the shaft and the magnetic flux is increased at the narrowest gap and reduced at the widest gap. It will be. This non-uniform distribution can also prevent the fluid from flowing evenly during operation, resulting in heat evaporation of such fluid or splashing from the gap region. Therefore, if the shaft is stationary or slowly rotating with respect to the housing, the ferrofluid will not be evenly distributed in the annular gap and will be drawn into the narrowest part of the gap and into the widest part. There is insufficient fluid left to maintain a proper seal strength. Such inadequate sealing strength can lead to a "burst" of the seal at a lower differential pressure threshold across the seal than would normally occur. U.S. Pat. No. 4,407,518, assigned to the applicant and issued on October 4, 1983, graphically illustrates bursts of ferrofluid.

The nature of ferrofluidic seals is that they "self-heal" to some extent even after such bursts. That is, ferrofluids released from the seal during a burst that are not more than a certain distance away from the seal and are within the reach of the magnetic field of the seal are drawn back into the effective seal area. However, for each burst, there is generally a net loss of ferrofluid from the seal, and therefore repeated seal overpressure can result in reduced sealing pressure performance. There is.

In addition, because of the inherent dynamic eccentricity of any rotating shaft, the contribution from shaft eccentricity due to inaccurate centering of the ferrofluidic seal is minimized. I have to. Very fast rotating shafts, or shafts that are relatively unevenly supported by bearings (e.g., so that the shaft can be extended over time), exhibit excessive dynamic eccentricity. Also,
Shafts supported by obsolete bearings may exhibit unacceptable dynamic eccentricity. Such dynamic eccentricity in particular gives rise to two significant problems. First, the shaft may come into contact with a portion of the seal and distort the seal, or cause a magnetic short circuit, adversely affecting its operation. The shaft is also damaged by contact with such seals. Second, if the shaft is most eccentrically displaced during rotation, the resulting non-uniform annular gap forms a ferrofluidic seal that is weaker at the widest portion of the gap. Therefore,
Bursts such as those described above can occur at the weakened portion of the seal. Therefore, accurate centering of the seal around the shaft is important to the operation of the ferrofluidic seal and is desirable in preventing shaft damage.

Accurate centering of the seal around the shaft is usually accomplished by accurately guiding (aligning) the bearings and seals that support the shaft within a common housing. The accuracy of this method is
It depends on the accuracy of the centering of the shaft within the housing and the accuracy of the surface on which the seal is guided.
Shaft / seal arrangements in this manner are preferably performed in one place to ensure overall accuracy.

In some cases, however, the seal cannot be accommodated in the housing and cannot be guided with respect to the housing in which the shaft is precisely mounted, so that the seal is close to the bearing with the correct relationship with respect to the shaft. Cannot be provided, and a recess for accommodating the seal cannot be provided in the housing in which the seal is provided, and it is inconvenient or impossible to verify the concentricity between the existing recess and the shaft, or It may not be possible to access the end of the shaft to slide the seal onto the shaft. Replacing a ferrofluidic seal when installing or replacing a ferrofluidic seal on an existing device that requires additional sealing performance, when repairing or replacing a component of the device that uses a ferrofluidic seal It is not uncommon to encounter either of these situations, sometimes, or "on the spot," that is, when performing other work away from precision machinery and assembly equipment. A prominent example is shown below. In essential oil pumps, it is becoming increasingly important to control any volatile gas that escapes as a result of the leakage of volatile liquids. The operation of the essential oil pump typically includes a shaft driven by a motor and supported by precision bearings in a first housing, the shaft having a second space through a mechanical surface seal and a space that serves as a maintenance space. An impeller is driven by the shaft in the second housing, passing into the housing, i.e. the pump area, for displacing a liquid such as gasoline. Mechanical surface seals are not bearings and do not support the shaft to any degree of positional accuracy. Mechanical surface seals rely on small leaks across the face of the seal to provide lubrication. State-of-the-art low-emission seals actually work with the vapor on their face, rather than a liquid. Thus, volatile vapors are slowly but continuously released into the maintenance space and atmosphere. It is advantageous to seal the part of the maintenance space directly surrounding the mechanical surface seal in order to suppress the gases from the volatile vapors, and a ferrofluidic seal is ideal for this purpose. However, there is no convenient means to accurately place the ferrofluidic seal on the mechanical surface seal enclosure, and mechanical surface seals require relatively frequent maintenance,
Removal and replacement of the ferrofluidic seal is essential in this application. In fact, it is desirable to provide a ferrofluidic seal of this kind in existing essential oil pumping stations and in many other existing sources of toxic gases, such as chemical plants, and thus applicable technology for "field" operations. Is especially desired.

One of the prior attempts to center the seal around the shaft in applications such as those described above.
One is to slide the seal over the shaft all the way to the housing, then slide the tapered tubular sleeve over the shaft, taper end first, and slide the sleeve over the seal and shaft. It involves pushing in between. The tapered sleeve concentrically interrupts between the seal and the shaft, thereby centering the seal around the shaft. This seal is then permanently affixed to the stator of the machine. Finally, the tubular sleeve is withdrawn.

Another attempt at the prior art involves wrapping a thin metallic shim material around the shaft prior to sliding the seal over the shaft. The shim material is placed concentrically and uniformly around the shaft to center the seal that slides over the shim material. After fixing the seal to the existing installation, the shim material is removed.

[0016]

These prior attempts at centering ferrofluidic seals have been associated with drawbacks and problems. In particular, attempts involving tubular sleeves and shim materials are cumbersome and time consuming. in addition,
Prior to securing the seal to the stationary stator, it is important that the tubular sleeve or shim material be accurately positioned in place between the seal and shaft to create a precise concentric air gap. Become. Precise positioning of the tubular sleeve and shim material cannot be easily achieved. As such, centering the seal requires a difficult and tedious procedure. Moreover, these centering methods are not compatible with preassembled cartridge-type seal configurations.

Further, the ferrofluid released from the ferrofluidic seal by the burst of the seal due to overpressure is in the vicinity of the seal so that the released ferrofluid is pulled back into the effective sealing area by the magnetic field. There is currently no way to retain.

Accordingly, the general object of the present invention is to center a ferrofluidic seal around a shaft,
It provides a self-powered mechanism that can be conveniently and quickly used, provides a mechanism for centering a ferrofluidic seal that is retrofitted around a shaft that is inaccessible at both ends, and provides a mechanism for Providing a mechanism for centering a ferrofluidic seal that can be left permanently in place and a centering mechanism for a ferrofluidic seal that can be easily removed after the seal is installed. Moreover, substantially the majority of the released ferrofluid is held within the reach of the magnetic field of the seal and pulled back into the effective seal area, minimizing the net loss of ferrofluid during bursts. , The burst pressure-based burst forces the seal to reduce the pressure performance of the seal due to such bursts to a minimum. To provide a means and mechanism for retaining the sexual fluid in the vicinity of the seal.

[0019]

[Means for Solving the Problems] The above-mentioned problems and problems,
The drawbacks are achieved and overcome by providing a centering ring that can be attached to the seal in a fixed relationship to the magnet and pole piece module. The centering ring engages the shaft when the seal is installed and centers the seal around the shaft. The centering ring includes an inner edge extending beyond the pole piece and in direct contact with the shaft. The centering ring can be configured so that it can be removed from the seal after it has been installed around the shaft, or it can be held in place during operation of the seal. The inner edge of the centering ring is designed to be gradually worn away by contact with the rotating shaft, or to be destroyed in a non-hazardous manner. The centering ring, which is configured to stay in place during operation,
It also serves the additional function of holding the ferrofluid released from the seal in the vicinity of the "burst" near the seal and causing it to be pulled back into the seal by a magnetic circuit, which can extend the life of the seal.

Other advantages, novel features and problems of the present invention will become apparent when the following detailed description of the invention is referred to in connection with the accompanying drawings.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a prior art two-stage ferrofluidic seal structure is shown. This is an annular magnet
It includes a modular seal 11 consisting of 18 and axially fixed annular pole pieces 14 and 16. The seal includes a housing 28 that axially surrounds the magnetically permeable shaft 12.
It is arranged in the recess 21 inside. It will be appreciated that in this and other embodiments, the shaft 12 can be solid or hollow and can be in a static or movable relationship with the housing 28. Therefore the shaft
12 rotates within a stationary housing 28, or the housing 28 rotates around a stationary shaft 12. The housing 28 can be part of the frame or stator of a stationary device such as a motor or pump with bearings (not shown) for centering the shaft. The module of seals is sealed in the recess 21 by fixed elastic seals or "O-rings" 23 and 25, which are preferably located on the outer edges of the two pole pieces 14 and 16, respectively. The O-rings 23 and 25 engage the inner wall of the recess 21 in a gas-tight manner. The pole pieces 14 and 16 are preferably arranged when the seal 11 is positioned around the shaft 12 and have a small gap or gap (22) between the inner edge of the pole piece and the outer surface of the shaft. And 24 respectively) are present radially (typically 0.001 to 0.004)
Inches (range 0.03 to 0.1 mm)). Ideally, when the module of seals is positioned and secured within the recess 21 of the housing, the seals are automatically centered around the shaft and supported by the housing. The shaft is rotationally driven by a motor or other means (not shown).

The shaft 12 and the pole pieces 14 and 16 are made of a magnetically permeable material so that the magnetic field generated by the magnet 18 follows the magnetic flux path F shown in FIG. The magnetic flux path F is
Extends across the gaps 22 and 24 between the inner edges of the pole pieces 14 and 16 and the shaft 12 to retain the ferrofluid 20 in the gaps 22 and 24, thereby causing a liquid O around the shaft 12. Form a ring seal.

As mentioned above, for the operation of the ferrofluidic seal, the pole pieces 14 and 16 are relatively accurately centered around the shaft 12 and the gaps 22 and 24 are relatively uniform in the radial direction. This is very important. The centering ring of the present invention has no hardware (as in the prior art embodiment of FIG. 1) that a device using such a seal is arranged to house and automatically center the seal, or the end of the shaft. It provides self-centering of the seal when the seal is installed around the shaft in applications where the shaft must be retrofitted due to inaccessible parts.

Referring now to FIG. 2A, the inner surface 110 of the pole piece accurately centered about the shaft 111.
A side view of is shown. X is the clearance between the shaft 111 and the inner surface 110 of the pole piece, ie the width of the annular gap in which the ferrofluid is retained to create the ferrofluid seal (not shown to scale). Is represented. FIG. 2 (b) shows the inner surface 110 of the pole piece non-concentrically provided around the shaft 111. Y represents the narrowest part of the annular gap and Z represents the widest part.
When this non-centered arrangement appears, the magnetic flux is much more concentrated in Y than in Z. as a result,
Ferrofluids are unevenly distributed in the annular gap, especially when the shaft and pole pieces are in a stationary relationship to each other,
In Y more ferrofluid is drawn into the gap and in Z less fluid remains in the gap. Therefore, the resulting ferrofluidic seal has poor pressure performance at Z. Generally, when Y is greater than 1/2 of X, that is, when the annular gap is at its narrowest portion, the shaft is perfectly centered within the pole piece (within 50% uniformity range). If it is wider than half the width of the gap, the resulting ferrofluid seal will work properly. If Y is less than 1/2 of X, then a problem occurs.

When the shaft is rotating relative to the pole pieces, the vibrations inherent in any rotating shaft complicate the situation, especially at high speeds and / or in the presence of significant overhanging of the shaft. Become. Figure 2 (c)
Shaft 111 when the shaft is stationary (solid line) and when the shaft vibrates during rotation (dotted line).
A pole piece 110 is shown which is slightly non-concentric around the circumference of the. It should be noted that, for purposes of illustration, only vibration of the shaft in one direction perpendicular to the longitudinal axis of the shaft is shown. When the shaft 111 is stationary, the annular gap is wide enough in the narrowest portion R to provide a proper seal.
However, when the shaft 111 rotates (and vibrates), the gap becomes narrow in the narrowest portion Q so as to make the seal unstable.

Referring to FIG. 3, a ferrofluidic seal module 10 is shown that includes an annular magnet 18, annular pole pieces 14 and 16, and a housing 100. The ferrofluidic seal module 10 and / or housing 100 is fitted with a centering ring 26 of the present invention, which provides centering of the seal around the shaft. The centering ring 26 is an annular ring that has an outer edge 33 that fits tightly within the housing 100 and an inner edge 31 that engages the shaft when the ferrofluidic seal module 10 is mounted around the shaft. And an inner portion 29 with. For purposes of illustration, centering ring 26 includes housing 100 and pole piece 1
It is in contact with both of 4. However, the centering ring 26 may be fixed to the housing 100 only, or to the pole piece 14 only, and as shown in the housing.
It will be appreciated that it may be secured to both 100 and pole piece 14. When the inner edge 31 engages the shaft 12, the seal is positioned such that the desired gap G is formed between the inner edge 35 of the pole pieces 14 and 16 and the outer surface 37 of the shaft. . In this and other embodiments, the gap G is a shaft and only one pole piece, two or more pole pieces, one or more ridges of multi-pole pieces, an annular magnet, or some combination thereof. It will be appreciated that it is desirable to generate during. Furthermore, it will be appreciated that in this and other embodiments, the centering ring as shown in FIG. 3 need not engage the shaft at the inner edge 31 throughout the ring. That is, the centering ring 26 may consist of a series of individual inner portions 29 extending inward to engage the shaft with a circumferential frequency sufficient to perform the function of centering. Once centered, the housing 100 can be provided to the housing 28 of another device. The annular centering ring 26 is a precision component that can be machined to precise tolerances to achieve any desired gap G, including in the range of a few thousandths of an inch. it can. As will be described below, various embodiments of the centering ring 26 are in view here.

One of the centering rings as shown in FIG.
In the embodiment, the centering function is performed and the housing 10
It is intended to be removed after the 0 has been secured to the housing 28 of another device. Illustratively, such centering rings are fairly rigid, and consist of aluminum, brass, steel or other fairly rigid, non-magnetically permeable material. The centering ring 26 can be removably secured to the ferrofluidic seal module 10 and / or the seal housing 100 by snap fit, groove fit, or other non-permanent means described below. The centering ring 26 of FIG. 3 has an L-shaped cross section and is rigid and sturdy within the housing, yet its length and inner edge at the inner portion 29 are precisely defined. However, it will be appreciated that the centering ring 26 may have other cross-sectional shapes and still operate according to the present invention.

Referring to FIG. 4, centering ring 26
Is shown in the direction of the arrow A in FIG. This embodiment is suitable for applications where the seal can be slid over the end of the shaft (ie the end of the shaft is accessible). As shown, the centering ring 26 includes an inner opening 30 through which the shaft 12 is threaded. The inner edge 31 of the centering ring is
It defines a circle with radius r1. Shown in dotted lines in FIG. 4 is the circle defined by the inner edges 35 of the pole pieces 14 and 16. This circle with the inner edge 35 has a radius r2. These circles due to the inner edges 31 and 35 are concentric and the radius r2 is larger than the radius r1. Therefore, almost r2 and r1
A gap G equal to the difference between and is created. in addition,
These circles due to the inner edges 31 and 35 are concentric with the circle (not shown) defined by the cross section of the outer surface 37 of the shaft.

Referring to FIG. 5, a side view of an alternative embodiment centering ring 32 is shown as viewed in the direction of arrow A in FIG. In this embodiment, centering ring 32 includes two substantially identical pieces 34 and 36.
Is a split centering ring with a small gap 38 between them. Since it is divided into two halves along its diameter, the centering ring 32 can be easily removed after its centering function has been performed. This split ring alternative embodiment configuration is useful when the solid centering ring, such as that shown in FIG. 4, cannot be removed from the circumference of the shaft due to the small amount of space available. . It should be noted that according to this embodiment, the two pieces 34 and 36 are simply clamped onto the shaft in a clamshell configuration. The number of pieces into which the ring is split to facilitate removal can be changed to suit the application, the pieces do not have to touch each other, and the pieces are placed around the inner surface of the seal. It will be appreciated that the placement can be substantially symmetrical or in any manner that facilitates accurate centering.

The centering ring may be secured to the ferrofluidic seal module and / or housing by means of appropriately prepared features of ferrofluidic seal module 10 and / or housing 100 itself. For example, as shown in FIG. 3, the housing includes a shoulder portion such that the centering ring fits within the shoulder portion and is thereby held in place. As shown, the outer edge 33 of the centering ring
Fit tightly to the shoulder 98 of the housing 100. Alternatively, as shown in FIG. 6, one of the pole pieces may have a similar shoulder in which the centering ring may fit. As shown, the outer edge 51 of the centering ring 26 is the shoulder of the pole piece 40.
It fits tightly against the 41.

If the components of the ferrofluidic seal module and the centering ring have contacting surfaces, these components are machined to precise tolerances to produce the desired uniform gap G. . However, due to the inaccuracies inherent in the machining process, perfect gap uniformity cannot be achieved. As described above with respect to FIG. 2, at least 50% uniformity is a goal and can be achieved with the centering ring of the present invention. The gap uniformity increases as the number of contact surfaces decreases. Therefore, one advantage of the embodiment shown in FIG. 3 is that the pole pieces and the centering ring are all relatively accurate relative to each other because they are similarly guided on the housing 100. It is to be centered (assuming that the surface of the housing 100 that engages the outer surface 33 of the centering ring is precisely machined). In this embodiment, the housing 100 should be concentric around the shaft 12. Any lack of concentricity in the housing 100
It is transmitted to the pole piece and the centering ring. One advantage of the embodiment shown in FIG. 6 is that when the centering ring 26 is guided directly on the pole piece 40 (there is only one contact surface), the pole piece 40 is better than the shaft 12. This means that good concentricity is guaranteed. The concentricity of the pole piece 16 depends on the alignment with the pole piece 40, according to this embodiment. However, if a one-step seal is desired, that is, pole piece 40 holds the ferrofluid and pole piece 16 acts as a flux enhancer (and generally not as close to the shaft as pole piece 40). In this case, this embodiment is the most advantageous.

FIG. 7 shows another means for securing the centering ring to the pole piece 14. As shown, the centering ring 26 is secured to the ferrofluidic seal module by threaded fasteners 42. Threaded fastener
42 is screwed to the pole piece 14 through the slot 27 of the centering ring 26. The slot 27 is wider than the body 43 of the threaded fastener 42 (as shown in FIG. 7) to allow adjustment of the position of the centering ring 26 with respect to the ferrofluidic seal module. Adjusting the position of the centering ring can compensate for any positional defects or inaccuracies in the components of the ferrofluidic seal.

FIGS. 8 to 11 show an alternative embodiment of the invention, in which the centering ring is adapted to the ferrofluidic sealing module in a properly designed interrelation in the seal housing and the centering ring itself. Fixed by connection features. In the embodiment of FIG. 8, a cord-shaped centering ring 56 is arranged in the recess 58 of the inwardly extending portion 60 of the housing 62. The recess 58 receives and retains the centering ring 56, which is to be removed from the ferrofluidic seal module after the centering function has been performed.

FIG. 9 is a side view of the centering ring of FIG. 8 seen from the direction of arrow B. As shown, the centering ring 56 has a cord-like shape, and when the seal is installed around the shaft, the cord-like centering ring 56 is wrapped around the shaft 12. Centering ring 56 has a handle 68 at one end, which is located outside a ferrofluidic seal (not shown). The other end 64
Abuts the centering ring at the location indicated by 69,
Centering ring completely surrounds shaft 12 (although centering ring 56 is shaft
Even if 12 is not completely surrounded, that is, if the other end 64 does not abut the centering ring at the position indicated by 69,
Centering ring can be achieved properly). This "stripped cord" shaped configuration of the centering ring allows the centering ring to be easily removed from the ferrofluidic seal module after the centering function is performed by pulling on the handle 68.

In the embodiment shown in FIG. 10, the centering ring 74 has two lips 76 which define a recess 77 and
Contains 78. The recess 77 receives and holds the inwardly extending portion 72 of the housing 70. The centering ring is thereby fixed with respect to the ferrofluidic sealing module. Between the inwardly extending portion 72 of the housing 70 and the outwardly projecting portion 80 of the centering ring 74,
A space 82 is created. This space allows the tool, eg the tip of a screwdriver (not shown), to be pushed into it after the centering function has been carried out and to allow the tool to remove the centering ring from its holding position. It is provided. It will be appreciated that the centering ring 74 need not have the same cross section as shown in FIG. 10 in all its parts. For example, lip 76
And 78 need not be present over all parts of the centering ring, but around the centering ring often enough to secure the centering ring 74 to the ferrofluidic seal for centering purposes. Only. In fact, the lip 76 is advantageously present only in selected portions of the centering ring 74 so that removal of the centering ring after use is not unacceptably difficult. Similarly, the portion 80 of the centering ring 74 need not be present throughout the ring, but is preferably present at a frequency such that removal of the ring is readily feasible.

FIG. 11 shows an embodiment in which the inwardly extending portion 86 of the housing 84 is provided with a lip 88 which is received in the recess 93 of the centering ring 92 and abuts against the lip 94. . The centering ring 92 is thereby fixed to the ferrofluidic seal module. After centering is performed, the centering ring 92
It can be removed from the ferrofluidic seal module by inserting the tool into the space 90 and removing the centering ring (as described above). The lip 88 of the housing 84 can be designed to break away upon removal of the centering ring and stay with the centering ring. As discussed above with respect to FIG. 10, the cross section of the centering ring 92 need not be as illustrated in FIG. 11 across the ring. For example, a series of individual tabs having a cross-section similar to that shown for the centering ring 92 in FIG. 11 may be placed in series around the shaft and attached to the portion 86 at separate points, thereby It can be used as an alternative to the conventional centering ring. Centering ring 92
Other embodiments can be envisioned for attachment to portion 86 of the. For example, instead of the recess 93 and lip 94 shown in FIG. 11, a protrusion from the centering ring 92, or another portion thereof, at various locations along the inwardly extending portion 86, as in other equivalent embodiments. In a similar manner, a "snap fit" can be made into the recess.

The centering ring configuration described above is designed to be removed after the ferrofluidic seal is centered and installed. If left in place, such centering rings could potentially rub against the rotating shaft, drag, heat, and possibly damage the shaft. According to another embodiment of the invention, the non-removable centering ring functions like the centering ring described above, while at the same time providing the additional advantage that it does not need to be removed for operation. The non-removable centering ring is formed of a suitable material such that movement of the rotating shaft results in rapid wear or fracture removal of the inner edge of the centering ring. In this way, dangerous contact with the shaft is eliminated after the centering feature is achieved.

A non-removable centering ring is shown in FIG. The centering ring 26 is made of abradable material 45 or its inner edge 31 is coated with such a material. Alternatively, the inner edge 31 can also be a separate member made of an abradable material and attached to the centering ring or housing.
This material 45 is used to provide accurate centering,
It has a relatively high stiffness, but has a low hardness compared to the material of the shaft to avoid damage to the shaft, and has a predictable wear rate for uniform wear.
Many such materials have been developed for similar wear applications such as mechanical seals, bushings, brake pads, chain guides. Examples of suitable materials for such use include carbon filled Teflon (CFT), polyimide, polyacetal, polybenzimidazole (PB).
I), polyether-ether ketone (PEEK), and ultra high molecular weight polyethylene (UHMWPE). These and other "engineering plastics" can be used in pure form or in glass, talc,
It can be used as a composition with graphite and fillers and / or reinforcing materials such as molybdenum disulfide, whereby the mechanical and wear properties are tailored to suit the particular application.

As an alternative to manufacturing the centering ring from wear material or coating the inner edge, the centering ring is designed to have an inner end that breaks away when in contact with a rapidly rotating shaft. can do. Such a centering ring is shown in FIG. As shown, the centering ring 44 has an inner peripheral edge 52 that is provided with a plurality of radial notches 45. The notches 45 define a plurality of fingers 46, each finger having an inner edge 54 at the inner peripheral edge 52 for engaging a rotating shaft. The resulting discontinuous inner peripheral edge 52 of the centering ring 44 is still sufficient to provide the function of centering. The radial fingers 46 are crushed away when they come into contact with the rotating shaft after performing the centering function. In particular, the fingers can be designed and shaped to form stress points in place, at which point the fingers are ruptured away in a predictable manner and fall in a predictable direction (which mechanical member or Do not touch human eyes).

Such a non-removable centering ring can serve an additional function in certain applications involving the pressurization of a ferrofluidic seal. In particular, when the ferrofluidic seal is subjected to excessive pressure, either intermittently or otherwise, some of the ferrofluid captured in the sealing gap will be forced out of the gap. That is, the seal may "burst" as described above.
Such loss of ferrofluid typically results in a seal with poor pressure performance. It is possible that the seal may lose all of its sealing ability after a number of overpressure cycles due to the loss of a significant amount of ferrofluid. However, if the ferrofluid that is displaced from the seal gap during overpressure is retained near the seal gap, it can be pulled back into the seal by magnetic attraction. Therefore, a means to physically hold the displaced ferrofluid in the vicinity of the seal gap during overpressure will increase the seal's ability to recover after each overpressure, thereby causing seal failure. Without, it is possible to withstand repeated overpressure events. Wear-type non-removable centering rings are the most effective way to hold ferrofluids by acting as a physical barrier to keep displaced ferrofluids close to the seal gap during pressurization. Can act as a means.

Alternatively, a ferrofluid retention device specially designed to perform this retention function can be employed. This is done, for example, by providing a block of material with an inner peripheral edge close to the circumference of the shaft, and this holding device in a very close relationship to the pole piece so that the ferrofluid that is pushed away from the seal during the burst is near the pole piece. In a position to allow the displaced ferrofluid to be pulled back into the effective portion of the seal by the magnetic field.

[0042]

The centering ring of the present invention is very useful for performing the centering function.
The centering ring is substantially between the inner surface of the pole piece (s), the magnet (s), or other components of the ferrofluidic sealing device, and the outer surface of the shaft. It is possible to generate a small gap that is uniform in the circumferential direction.

The ferrofluidic seal with centering ring of the present invention is particularly useful when it is required to mount the seal to existing equipment. These cases are especially prevalent when ferrofluidic seals are added to devices that were not originally designed for such ferrofluidic seals. Included in such examples are centrifugal pumps that were not originally designed for ferrofluidic seals, but could later be fitted with ferrofluidic seals to eliminate leaks. There is. Another such situation is when a ferrofluidic seal is installed (to improve hermeticity) to replace an existing seal, or in series with another seal that is slightly leaking. It happens in some cases. Included in this latter case of a double seal is a robot actuator designed for use in ultra high vacuum processing of semiconductor wafers. For such existing installations, the ferrofluidic seal including the centering ring of the present invention is mounted onto the rotating shaft and centered automatically. The centering ring of the present invention additionally provides for ease of mounting.

It will be appreciated that the centering mechanism of the present invention may be used in a variety of applications where a member such as a shaft must be centered within another member such as a housing. That is, the centering ring of the present invention is not limited to use in a ferrofluidic seal.

Those skilled in the art will appreciate that all parameters described herein are intended to be exemplary and the actual parameters will depend on the particular application for which the seal is being used. You will easily understand that. Therefore, the above-mentioned embodiments are presented only as examples, and within the scope of the claims and the equivalent thereof, the present invention can be carried out in a form different from that specifically described above. Will be understood.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a prior art ferrofluidic seal operating around a rotating shaft.

FIG. 2 is a side view of the inner edge of a pole piece concentrically and non-concentrically provided with the shaft.

FIG. 3 is a cross-sectional view of a ferrofluidic seal showing a centering ring according to one embodiment of the present invention.

4 is a side view of a centering ring according to an embodiment of the present invention, as viewed in the direction of arrow A in FIG.

5 is a side view of a centering ring according to an alternative embodiment of the invention, as viewed in the direction of arrow A in FIG.

FIG. 6 is a cross-sectional view of a ferrofluidic seal according to another alternative embodiment of the present invention.

FIG. 7 is a cross-sectional view of a ferrofluidic seal according to yet another alternative embodiment of the present invention.

FIG. 8 is a cross-sectional view showing only the upper half of a ferrofluidic seal according to yet another alternative embodiment of the present invention.

9 is a side view of the centering ring of the alternative embodiment of FIG. 8. FIG.

FIG. 10 is a cross-sectional view showing only the upper half of a ferrofluidic seal according to yet another alternative embodiment of the present invention.

FIG. 11 is a cross-sectional view showing only the upper half of a ferrofluidic seal according to yet another alternative embodiment of the present invention.

FIG. 12 is a cross-sectional view of a ferrofluidic seal showing a centering ring having an abradable inner edge, according to one embodiment of the present invention.

13 is a side view of a centering ring according to yet another embodiment of the present invention, as viewed in the direction of arrow A in FIG.

[Explanation of symbols]

10 ferrofluid seal module 11 seal 12 shaft 14, 16, 40 pole piece 18 magnet 26, 32, 44, 56, 74, 92 centering ring 28, 62, 70 housing 29 inner portion 31 inner edge portion 33, 51 outer Edge 35 Inner Edge 37 Outer Surface 38 Gap 42 Threaded Fastener 45 Abrasive Material 46 Finger 52 Inner Edge 54 Inner Edge 68 Handle

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 21, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 4]

[Figure 5]

[Figure 9]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 6]

[Figure 7]

[Figure 8]

[Figure 10]

FIG. 11

[Fig. 12]

[Fig. 13]

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Thomas J. Black, Jr. Wire Hawk Road, 03054, Mary Hackshire, New Hampshire, USA 84 (72) Inventor Paul E. McMahan, Louisiana, USA 70785 Walker, Coriel 11996 (72) Inventor Larry A. Hafford, Vila Shera Rhod, 15820 Valley Center, California, USA 15350 (72) Inventor David Tie Mooney, California, California 94903 San Rafael, Russ. Galinus Avenue 1065 (72) Inventor Robert Sea Watkins Mississippi, USA 39568 Pass Kagola, Oli Vice load 8908

Claims (41)

[Claims] 1. A centering ring for use with a ferrofluidic seal forming a seal around a shaft having an outer surface, the ferrofluidic seal generating at least a magnetic field axially disposed about the shaft. A magnet and at least one pole piece, the pole piece extending toward the shaft to form a gap between the pole piece and the shaft, the gap being ferromagnetic; Fluid fillable, wherein the centering ring has a block of material having an inner peripheral edge that contacts the outer surface of the shaft, and the gap when the inner peripheral edge of the block of material contacts the outer surface of the shaft. So that the centering ring is fixed relative to the pole piece so that is substantially uniform around the shaft. Consisting of, centering ring. 2. The inner peripheral edge of the block of material defines a first circle and the outer surface of the shaft defines a second circle.
The centering ring of claim 1, wherein the circles are concentric. 3. A block of material is a wear talling ring. 4. An inner peripheral edge of the block of material defines a plurality of fingers, the fingers being arranged on the inner peripheral edge in a shape such that they will be destroyed by contact with the shaft during rotation of the shaft. The centering ring according to claim 1, which is provided. 5. The means for providing a centering ring comprises means for permanently providing a centering ring.
The centering ring according to claim 1. 6. The centering ring of claim 1, wherein said means for providing a centering ring comprises means for non-permanently providing a centering ring. 7. The centering ring of claim 1, wherein the means for providing a centering ring includes means for adjusting the position of the centering ring with respect to the pole piece. 8. The centering ring of claim 7 including a centering ring and a threaded fastener that is threadedly attached to the pole piece through the groove. 9. The centering ring of claim 1, wherein the means for providing a centering ring includes a shoulder portion defined in the pole piece for receiving the centering ring. 10. The centering ring of claim 1, wherein the means for providing a centering ring includes a shoulder portion defined in the seal housing for receiving the centering ring. 11. A centering ring is defined in the non-housing and includes a recess for receiving the centering ring.
The centering ring according to claim 6. 12. The centering ring has a cord-like shape, and the means for non-permanently providing the centering ring further comprises a handle attached to the centering ring to remove the centering ring during pulling. Centering ring. 13. The centering ring of claim 6 wherein said means for non-permanently providing a centering ring includes a recess defined in the centering ring to receive a leg of the seal housing. 14. The means for non-permanently providing a centering ring includes a recess defined in the centering ring to receive a lip defined in the seal housing, the lip breaking when the centering ring is removed. 7. The centering ring of claim 6, which is removed. 15. The seal undergoes periodic bursts due to overpressure, the inner peripheral edge of the block of material comprising:
The centering ring of claim 1, configured and arranged to retain a majority of the ferrofluid that is displaced from the seal during a burst in a magnetic field such that it is withdrawn back into the seal. 16. A centering ring for use with a ferrofluidic seal forming a seal around a shaft having an outer surface, the ferrofluidic seal producing at least a magnetic field axially disposed about the shaft. A magnet and at least one pole piece, the pole piece extending toward the shaft to form a gap between the pole piece and the shaft, the gap being ferromagnetic; Filled with a fluid, wherein the centering ring comprises a block of material having an annular inner peripheral edge in contact with the outer surface of the shaft, and an inner peripheral edge of the block of material in contact with the outer surface of the shaft. The centering ring is fixed with respect to the pole piece so that the gap is substantially uniform around the shaft. Consisting of Hisashi to provide means, centering ring. 17. The centering ring of claim 16, wherein the block of material comprises an abrasive material. 18. An inner peripheral edge of the block of material defines a plurality of fingers, the fingers being arranged on the inner peripheral edge in a shape such that they will be destroyed when they come into contact with the shaft during rotation of the shaft. The centering ring according to claim 16, which is provided. 19. The centering ring of claim 16 wherein said means for permanently providing a centering ring comprises a threaded fastener that is threadedly attached to said pole piece through the centering ring. 20. The centering ring of claim 16, wherein said means for permanently providing a centering ring includes a shoulder portion defined in said pole piece for receiving a centering ring. 21. The centering ring of claim 16 wherein said means for permanently providing a centering ring includes a shoulder portion defined in the seal housing for receiving the centering ring. 22. The seal undergoes periodic bursts due to overpressure, and the inner peripheral edge of the block of material comprises:
17. The centering ring of claim 16, configured and arranged to retain a majority of the ferrofluid that is displaced from the seal upon burst into a magnetic field so that it is withdrawn back into the seal. 23. A centering ring for use with a ferrofluidic seal forming a seal around a shaft having an outer surface, the ferrofluidic seal producing at least a magnetic field axially disposed about the shaft. A magnet and at least one pole piece, the pole piece extending toward the shaft to form a gap between the pole piece and the shaft, the gap being ferromagnetic; Fluid-filled, the centering ring having at least two blocks of material arranged adjacent to each other having an annular inner peripheral edge in contact with the outer surface of the shaft, and of the block of material The centering is such that the gap is substantially uniform around the shaft when the inner peripheral edge contacts the outer surface of the shaft. Comprising a non-permanent providing means in a fixed relationship ring against the pole piece, the centering ring. 24. The centering ring of claim 23, wherein the means for non-permanently providing a centering ring includes a shoulder portion defined in the pole piece for receiving the centering ring. 25. The centering ring of claim 23, wherein said means for non-permanently providing a centering ring includes a recess defined in the seal housing to receive the centering ring. 26. The means for non-permanently providing a centering ring comprises a recess defined in the centering ring for receiving a leg of a seal housing.
Centering ring. 27. The means for non-permanently providing a centering ring includes a recess defined in the centering ring to receive a lip defined in the seal housing, the lip breaking when the centering ring is removed. 24. The centering ring of claim 23, which is removed. 28. The seal undergoes periodic bursts due to overpressure, and the inner periphery of the block of material comprises:
24. The centering ring of claim 23, configured and arranged to retain a majority of the ferrofluid that is displaced from the seal upon burst into a magnetic field so that it is withdrawn back into the seal. 29. A sealing device configured to slide around a magnetically permeable shaft to provide a seal, the at least one magnet axially disposed around the shaft to generate a magnetic field, At least one disposed axially around the shaft
Two pole pieces, the pole pieces extending toward the shaft to form a gap between the pole piece and the shaft that can be filled with a ferrofluid; and an inner side that contacts the outer surface of the shaft. A centering ring having a peripheral edge and fixed to the pole piece such that the gap is substantially uniform around the shaft when the inner peripheral edge of the centering ring contacts the outer surface of the shaft. And a means for providing the centering ring in relation to each other. 30. The means for providing a centering ring comprises means for permanently providing a centering ring.
The sealing device according to claim 29. 31. The sealing device of claim 29, wherein said means for providing a centering ring comprises means for non-permanently providing a centering ring. 32. The sealing device of claim 31, wherein the means for providing a centering ring includes means for adjusting the position of the centering ring with respect to the pole piece. 33. The sealing device of claim 32, wherein said means for providing a centering ring comprises a threaded fastener screwed to said pole piece through the centering ring. 34. The sealing device of claim 29, wherein said means for providing a centering ring comprises a shoulder defined in said pole piece for receiving a centering ring. 35. The sealing device of claim 29, wherein said means for providing a centering ring comprises a shoulder portion defined in the seal housing for receiving the centering ring. 36. The sealing device of claim 31, wherein said means for non-permanently providing a centering ring comprises a recess defined in the seal housing for receiving the centering ring. 37. The centering ring has a cord-like shape, and the means for non-permanently providing the centering ring further comprises a handle attached to the centering ring to remove the centering ring upon pulling. Sealing device. 38. The means for non-permanently providing a centering ring comprises a recess defined in the centering ring for receiving a leg of a seal housing.
Sealing device. 39. The means for non-permanently providing a centering ring includes a recess defined in the centering ring to receive a lip defined in the seal housing, the lip breaking when the centering ring is removed. 32. The sealing device of claim 31, which is removed. 40. The seal undergoes periodic bursts due to overpressure, and the inner peripheral edge of the block of material comprises:
30. The sealing device of claim 29, configured and arranged to retain a majority of the ferrofluid that is displaced from the seal during a burst in a magnetic field such that it is withdrawn back into the seal. 41. A ferrofluidic retainer for use with a ferrofluidic seal for forming a seal having an effective seal area about a shaft having an outer surface, the ferrofluidic seal being disposed about the shaft. A magnetic field generating at least one magnet and at least one annular pole piece, the at least one pole piece extending toward the shaft between the pole piece and the shaft. A gap in which the gap is fillable with a ferrofluid, the device comprises a block of material having an inner peripheral edge proximate to the outer surface of the shaft, and pushing out of the seal upon bursting due to overpressure. The retained ferrofluid is held in a position near the pole piece and the displaced ferrofluid is drawn into the effective seal area by the magnetic field. Returned As, and means provided in the vicinity of a block of said material in said pole piece relationship apparatus.